client: fix fuse client hang because its pipe to mds is not ok

If fuse client session had been killed by mds and the mds daemon restart
or hot-standby switch happens right away but the client did not receive
any message from monitor due to network or other whatever reason untill
the mds become active again.Thus cause client didn't do closed_mds_session
lead the seession still is STATE_OPEN but client can't send any message to
mds because its pipe is not ok.So we should close the stale session so that
it can be reopened again.

Fixes: http://tracker.ceph.com/issues/36079
Signed-off-by: Guan yunfei <yunfei.guan@xtaotech.com>

src/client/Client.cc

@@ -2614,6 +2614,7 @@ void Client::handle_fs_map_user(MFSMapUser *m)
 
 void Client::handle_mds_map(MMDSMap* m)
 {
+  int old_inc = 0, new_inc = 0;
   if (m->get_epoch() <= mdsmap->get_epoch()) {
     ldout(cct, 1) << __func__ << " epoch " << m->get_epoch()
                   << " is identical to or older than our "
@@ -2666,6 +2667,13 @@ void Client::handle_mds_map(MMDSMap* m)
     if (!mdsmap->is_up(mds)) {
       session->con->mark_down();
     } else if (mdsmap->get_addrs(mds) != session->addrs) {
+      old_inc = oldmap->get_incarnation(mds);
+      new_inc = mdsmap->get_incarnation(mds);
+      if (old_inc != new_inc) {
+        ldout(cct, 1) << "mds incarnation changed from "
+		      << old_inc << " to " << new_inc << dendl;
+        oldstate = MDSMap::STATE_NULL;
+      }
       session->con->mark_down();
       session->addrs = mdsmap->get_addrs(mds);
       // When new MDS starts to take over, notify kernel to trim unused entries
@@ -2676,6 +2684,11 @@ void Client::handle_mds_map(MMDSMap* m)
       continue;  // no change
 
     session->mds_state = newstate;
+    if (old_inc != new_inc && newstate > MDSMap::STATE_RECONNECT) {
+      // missed reconnect close the session so that it can be reopened
+      _closed_mds_session(session);
+      continue;
+    }
     if (newstate == MDSMap::STATE_RECONNECT) {
       session->con = messenger->connect_to_mds(session->addrs);
       send_reconnect(session);

src/mds/MDSMap.h

@@ -616,6 +616,16 @@ class MDSMap {
     }
   }
 
+  /**
+   * Get MDS rank incarnation if the rank is up, else -1
+   */
+  int get_incarnation(mds_rank_t m) const {
+    std::map<mds_rank_t, mds_gid_t>::const_iterator u = up.find(m);
+    if (u == up.end())
+      return MDS_GID_NONE;
+    return get_inc_gid(u->second);
+  }
+
   int get_inc_gid(mds_gid_t gid) const {
     auto mds_info_entry = mds_info.find(gid);
     if (mds_info_entry != mds_info.end())